Piston



H. S. HEWITT March 10, 1936;

PISTON Filed Aug. 20, 1932 Patented Mar. 10, 1936 UNITED STATES PATENT OFFICE PISTON Application August 20, 1932, Serial No. 629,709- In Great Britain December 4, 1931 1 Claim.

This invention isfor improvements in or relating to pistons, and particularly, but not exclusively, to the kind of piston for internal-combus skirt is formed with a slot extending over each gudgeon-pin boss for the full width thereof, leaving the ring carrying portion of the piston continuous with the skirt between the gudgeon-pin bosses, a web is arranged to extend from each of the bosses to the crown of the piston, which webs are spaced away for the greater part of their length from the side wall of the piston, and a longitudinal slot is' arranged to extend from each of the aforesaid slots over the gudgeon-pin bosses along the length of the skirt and are arranged completely to sever the skirt along the whole of their length and permits the skirt to expand and contract circumferentially. It will be appreciated with this arrangement that each gudgeon-pin boss is supported on a flexible panel and it has been found that this arrangement assists in preventing the piston from becoming unduly distorted due to unevenstresses. It is usually found that the piston becomes distorted particularly in the region of the gudgeon-pin bosses, and it has been necessary to counteract this distortion by recessing the walls of the piston in these regions. In the construction of the present invention it has been found unnecessary to provide such recesses, and the surface of the skirt of the piston may be completely cylindrical.

A feature of the invention consists in that the continuation of the slot is arranged to terminate short of the open end of the skirt of the piston.

A further feature of the invention consists in that the slot over the gudgeon-pin bosses extends circumferentially, and in that additional circumferentially-extending slots are arranged near the open end of the skirt, and longitudinal slots are arranged to extend between the two sets of circumferential slots.

In any of the arrangements referred to above, a feature of the invention consists in that a longitudinal slot is arranged to extend from one end only of the circumferential slots. Alternatively, longitudinal slots are arranged to extend from a point intermediate of the ends of the circumferential slots, or two longitudinal slots may be arrangedto extend one from each end of a circumferential slot. The slots may be inclined engthwise of the piston with respect to the axis thereof and maybe of different lengths.

A still further feature of the invention consists in that the circumferentialslot situated over the gudgeon-pin bossmerges in a smooth 5 curve into the longitudinal slot extending therefrom.

- The following is a description of a number of embodiments of the invention as applied to pistons for internal-combustion engines.

Reference is made to the accompanying drawing in which Figure l is an elevation of a piston of the kind having internal webs joining the gudgeon-pin bosses with the inside of the crown of the piston and shows the method of slotting according to the invention;

Figure 2 is a. longitudinal section in a plane containing the axis of the piston and the axis 0 the gudgeon-pin bosses;

Figure 3 is a longitudinal section in a plane at right angles to that of Figure 2 and also containing the axis of the piston;

Figure 4 is a section on the line 44 of Figure 1;

Figure 5 is a section on the line 55 of Figure 2.

Like reference numerals indicate like parts in the several figures of the drawing.

The piston is shown as having webs l0 connecting the piston head II with the skirt 12.

Over each gudgeon-pin boss l3 there is a circumferential slot I4 which is arranged in a piston-ring-groove 9 as described in British Patent Specification No. 33,553/31 and cuts completely through the wall of the piston.

From one end of each circumferential slot [4 is a longitudinal slot l5 extending to a position near the bottom of the piston skirt but terminating short of the bottom as shown clearly in Figures 1 and 3. The two slots l5 are preferably slightly inclined towards the axis of the piston and are conveniently both on the same side thereof so that they converge slightly towards one another as they extend from the bottom of the skirt towards the piston.

There may be a similar slot from the other end of each circumferential slot !4 but generally it is found that a slot at one end onlyis sufficient. By these means the gudgeon-pin bosses are supported on a flexible panel.

There may be other circumferential slots such .as I6 situated between the slots I4 and it will be appreciated that adjacent'extremities of all the slots will be separated by solid portions of 5 the piston walls. Longitudinal slots may extend also from the slot l6 if desired and such longitudinal slots may extend completely through the bottom of the piston skirt.

Further, by means of a trepanning tool a cut such as I! (shown in dotted lines) is formed in the gudgeon-pin boss and it may extend only partially around the boss, as shown on the right of Figure 2, or it may extend completely around as on the left-hand side of that figure. In the latter case each gudgeon-pin boss will comprise virtually two aligned bearing portions separated by the out such as ll.

The demands on piston performance expected today from engine builders may be briefly summarized as:--

(1) Simple one-piece construction.

(2) Freedom from trouble on the test bench.

(3) Freedom from seizure or slap under service conditions.

(4) Maintenance of low oil consumption in between necessary engine overhaul periods.

Pistons of known form do not as a rule satisfy all these conditions but they are satisfied by a piston according to the present invention because it is- (a) Sufiiciently flexible to allow of distortion without necessity of relieving any portion of the piston.

(b) By the present invention a flexible panel is provided around the gudgeon-pin bosses which is sufiiciently flexible to allow for distortion under running conditions due to temperature and load reaction on the gudgeon-pin, while at the same preventing wear which would eventually lead to excessive oil consumption. The elimination of this relative motion is due to the fact that a comparatively tight-fitting piston can be utilized thereby avoiding oscillation within the cylinder. As such relative motion between the rings and the grooves is substantially eliminated the rings and ring-groove wear will be substantially reduced and consequently the escape of oil past the pistonrings will be largely eliminated.

I claim:-

A piston for an internal-combustion engine comprising a skirt formed with a slot over each gudgeon-pin boss, and with a longitudinal slot extending from each of the aforesaid slots over the gudgeon-pin bosses along the length of the skirt, and webs extending from the inside of the crown of the piston to the inside of said skirt, which gudgeon-pin bosses are arranged to extend between the inside face of the skirt, and said webs, by which two parts they are supported, and are divided into two parts by a circumferentially extending slot.

HERBERT STAYTON HEWITT. 

